Acquired aphasia is language loss resulting from stroke or other brain insult. It is a chronic disability that affects more than one million adult Americans, robbing each of the ability to express his or her language competence. The heterogeneous presentation of aphasia poses a challenge for diagnosis, measurement, and treatment of this devastating condition. This long-running grant endeavors to explain the many faces of aphasia from a theoretical perspective. Its methods and models have spawned new forms of assessing and treating aphasia, and offshoot grants supporting clinical trials and rehabilitation research infrastructure. Continuing goals of this project are to explain aphasic impairments in terms of psycholinguistic processing models, and to refine such models through the use of computational methods. This proposal adds a new goal: to further the understanding of brain-language relationships by combining the psycholinguistic description of production impairments with state-of-the art lesion-analysis methods. The proposal is presented in 2 parts. Part 1 advances the understanding of single-word production impairments using data and models developed in past work. Products developed in Part 1 will facilitate clinicians'and researchers'access to our methods and data. Part 2 focuses on the regulation of competitive word selection, and how impairment in such regulation contributes to the sentence-production impairments in agrammatism and other aphasia presentations. Studies in Part 2 address alternative models of competitive word selection and the putative role of one particular brain region - the left inferior frontal gyrus. Specific aims for Parts 1 and 2 are framed in terms of anticipated psycholinguistic, anatomical, and computational advances. If successful, this project will advance the understanding of how damage to specific brain networks disrupts the stages and processes of word retrieval and the regulation of sequential word selection. This research is relevant to the diagnosis of acquired disorders of language, the mapping of language functions in the human brain, and the development of theoretically motivated rehabilitation strategies.